From: Guillaume Nault <gnault@redhat.com>
To: "Pali Rohár" <pali@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>,
Paul Mackerras <paulus@samba.org>,
"David S. Miller" <davem@davemloft.net>,
linux-ppp@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ppp: Add rtnl attribute IFLA_PPP_UNIT_ID for specifying ppp unit id
Date: Wed, 11 Aug 2021 19:19:18 +0200 [thread overview]
Message-ID: <20210811171918.GD15488@pc-32.home> (raw)
In-Reply-To: <20210810160450.eluiktsp7oentxo3@pali>
On Tue, Aug 10, 2021 at 06:04:50PM +0200, Pali Rohár wrote:
> On Tuesday 10 August 2021 17:39:41 Guillaume Nault wrote:
> > On Mon, Aug 09, 2021 at 09:31:09PM +0200, Pali Rohár wrote:
> > > Better to wait. I would like hear some comments / review on this patch
> > > if this is the correct approach as it adds a new API/ABI for userspace.
> >
> > Personally I don't understand the use case for setting the ppp unit at
> > creation time.
>
> I know about two use cases:
>
> * ppp unit id is used for generating network interface name. So if you
> want interface name ppp10 then you request for unit id 10. It is
> somehow common that when ppp interface has prefix "ppp" in its name
> then it is followed by unit id. Seems that existing ppp applications
> which use "ppp<num>" naming expects this. But of course you do not
> have to use this convention and rename interfaces as you want.
Really, with the netlink API, the interface name has to be set with
IFLA_IFNAME. There's no point in adding a new attribute just to have a
side effect on the device name.
> * Some of ppp ioctls use unit id. So you may want to use some specific
> number for some network interface. So e.g. unit id 1 will be always
> for /dev/ttyUSB1.
But what's the point of forcing unit id 1 for a particular interface?
One can easily get the assigned unit id with ioctl(PPPIOCGUNIT).
> > I didn't implement it on purpose when creating the
> > netlink interface, as I didn't have any use case.
> >
> > On the other hand, adding the ppp unit in the netlink dump is probably
> > useful.
>
> Yes, this could be really useful as currently if you ask netlink to
> create a new ppp interface you have to use ioctl to retrieve this unit
> id. But ppp currently does not provide netlink dump operation.
>
> Also it could be useful for this "bug":
> https://lore.kernel.org/netdev/20210807132703.26303-1-pali@kernel.org/t/#u
This patch itself makes sense, but how is that related to unit id?
> And with unit id there also another issue:
> https://lore.kernel.org/netdev/20210807160050.17687-1-pali@kernel.org/t/#u
This patch shows why linking unit id and interface name are a bad idea.
Instead of adding more complexity with unit id, I'd prefer to have a
new netlink attribute that says "don't generate the interface name
based on the unit id". That's how the original implementation worked by
the way and I'm really sad I accepted to change it...
> But due to how it is used we probably have to deal with it how ppp unit
> id are defined and assigned...
>
next prev parent reply other threads:[~2021-08-11 17:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-07 16:37 [PATCH] ppp: Add rtnl attribute IFLA_PPP_UNIT_ID for specifying ppp unit id Pali Rohár
2021-08-09 19:25 ` Jakub Kicinski
2021-08-09 19:31 ` Pali Rohár
2021-08-10 15:39 ` Guillaume Nault
2021-08-10 16:04 ` Pali Rohár
2021-08-11 17:19 ` Guillaume Nault [this message]
2021-08-11 17:54 ` Pali Rohár
2021-08-12 9:19 ` Guillaume Nault
2021-08-12 14:09 ` Pali Rohár
2021-08-12 19:12 ` Guillaume Nault
[not found] ` <BN0P223MB0327A247724B7AE211D2E84EA7F79@BN0P223MB0327.NAMP223.PROD.OUTLOOK.COM>
2021-08-10 17:16 ` Pali Rohár
2021-08-10 18:11 ` James Carlson
2021-08-11 17:38 ` Guillaume Nault
2021-08-11 18:04 ` Pali Rohár
2021-08-12 9:28 ` Guillaume Nault
2021-08-12 13:48 ` Pali Rohár
2021-08-12 18:26 ` Guillaume Nault
2021-08-12 19:04 ` Pali Rohár
2021-08-16 16:11 ` Guillaume Nault
2021-08-16 16:23 ` Pali Rohár
2021-08-17 16:05 ` Guillaume Nault
2021-08-17 16:21 ` Pali Rohár
2022-07-09 12:09 ` Pali Rohár
2022-07-12 17:34 ` Guillaume Nault
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